This invention relates to the casting of concrete, especially the in situ casting of large areas of concrete. Such casting is useful for example in the formation of warehouse floors, car parks and similar open areas, roadways and paths. Particularly it relates to a screed rail which divides such areas into discrete regions, but remains part of the laid area.
Large areas of concrete have traditionally been laid in "patchwork" fashion. Adjacent discrete first regions are cast in a first stage against shuttering which is removed after the regions of concrete have at least partially cured. In a second stage, remaining vacant regions are cast against and between the first regions to complete the total area of concrete to the cast. The first regions define at least part of the boundaries of the regions in the second stage, so that separate shuttering is not needed within the total area and the cast concrete is substantially continuous. This technique is time-consuming as at least two curing stages must be accommodated. Further, the machinery used for tamping or vibrating the cast but not cured concrete in the first stage must be moved between the discrete first regions.
In order to reduce the number of casting stages necessary in the casting of large areas of concrete, methods have been proposed in which the shuttering used becomes a permanent part of the cast layer. Screed rails, usually of pre-cast concrete, are first laid to define a grid of castable regions into which concrete can be poured in a single stage. The screed rails provide support for tamping and vibrating machinery which can thus be applied to the whole area cast, again in a single stage. Two such techniques are disclosed in Swiss Patent Specification No. 545393 and International Patent Publication No. WO 81/02600.
The pre-cast concrete screed rails described in the above Patent publications have in common some primary disadvantages. Being of relatively complex cross-section, they are neither easily cast nor stacked for transportation, and further, they are relatively fragile. As a consequence, particularly because of the stacking problems, they can become cracked or chipped and quite a large proportion of a load of rails must commonly be rejected when the load reaches a site. The stacking problem can also result in the total loss of a load if it is not very carefully assembled and secured on a truck or lorry.
Heretofore, a screed rail of solid, substantially rectangular cross-section has also been either too thin to function with sufficient stability in the casting site, or too large for easy transportation. It is also desirable to define in the screed rail a keying mechanism for the concrete cast against it, and this is achieved in the known rails by forming the screed rail with a recess between enlarged upper and lower edges.
Screed rails of the present invention type are usually of cast concrete which can be reinforced and/or pre-stressed in conventional manner. Where the concrete area to be laid is to be reinforced, provision can be made for reinforcement to be carried through the rails by the formation of openings therein, for example, normally between the parallel sides thereof. International Patent Publication No. WO 81/02600 referred to above discloses the provision of holes for the passage of connecting devices. However, the provision of holes can complicate the casting of the rail.